1. Field of the Invention
The present invention generally relates to aqueous fluid compositions for use in forming abrasive slurries. The aqueous fluid compositions are useful for forming loose-abrasive machining slurries and, more particularly, wire saw slurries.
2. Background
Wire saws are extensively used to slice silicon for solar and electronics applications. They are also used for slicing a variety of other compound semiconductor materials including sapphire, GaAs, InP, and SiC, optical materials such as quartz glass and crystal, and hard and brittle materials such as ceramics.
A wire saw generally includes a plurality of wires oriented under tension. The wires are driven simultaneously as an abrasive slurry is supplied between the wires and workpiece. The workpiece is forced through the wires as the slurry acts to abrade the workpiece into a plurality of pieces. This method allows for the production of large numbers of sliced pieces of particular thickness, flatness, and surface smoothness.
During wire saw cutting, the wire does not do the cutting, but rather it acts to transport the abrasive slurry, which does the cutting. This type of process is called “loose-abrasive machining.” Other examples of loose-abrasive machining include ultrasonic machining, water-jet cutting, and sandblasting.
The slurry is a suspension of abrasive particles in a fluid composition, also sometimes referred to as a “lubricant”, “vehicle” or “carrier”. As the abrasives, materials such as silicon carbide (SiC), diamond, and boron carbide (B4C) have been used. Nonaqueous slurries have been employed, wherein the fluid composition predominantly contains mineral oil in which the abrasives are dispersed at a ratio of about 1:1 based on weight. Water soluble slurries have also been employed, wherein the fluid composition predominantly contains a water soluble glycol (e.g., polyethylene glycol (PEG), ethylene glycol, and polyoxyethylene glycol) in which the abrasive particles are dispersed.
While mineral oil provides good lubricating and cutting properties, it possesses poor cooling performance. Further, because mineral oil is not water soluble, organic solvents and specialized detergents are required to clean the mineral oil from the cut pieces. Due to poor cooling performance, disposal restrictions, and post cleaning difficulties, alternatives to mineral oil are needed.
While glycols, such as PEG, offer some benefits over mineral oil, these materials are very costly and they present problems with the amounts and methods of disposal available. Further, glycols have high viscosities that lead to increased drag forces on the wafer. Such high drag forces can lead to breakage of cut pieces during thin slicing.
It would, thus, be highly desirable to develop improved fluid compositions for use in forming abrasive slurries, particularly wire saw slurries.